NFC (Near Field Communication), an international standard, has been known as one example of the technology of short-range wireless communication. The NFC has gained growing acceptance primarily in Asian countries for use in such applications as payment of fares for public transportation, accounting, and authentication, for example.
The NFC is used extensively in smartphones. In the future, the technology is expected to find its way into smaller devices such as wearable devices. Furthermore, miniaturization of the parts for implementing the NFC (-based) communication capability is expected so that the NFC will be applied to downsized devices.
The NFC communication takes place using magnetic fields between an R/W (Reader/Writer) and a transponder such as an IC (Integrated Circuit) card communicating with the R/W.
More specifically, the R/W and the transponder communicate with each other through electromagnetic induction between their coils acting as antennas.
Incidentally, the coils acting as the antennas in the R/W and the transponder constitute a resonant circuit each. The resonance frequency of the resonant circuit varies typically with variations in the parts making up the resonant circuit. If the resonance frequency deviates from its normal value (design value), the communication performance (characteristics) such as communicable distance deteriorates.
In view of that, techniques have been proposed for correcting the resonance frequency. The techniques involve transmitting an adjustment signal, receiving the transmitted signal, and adjusting a variable capacitor in accordance with the received signal to improve the deterioration of the communication performance typically attributable to variations in parts (e.g., see PTL 1).